A common use for security seals is for sealing closed the mouth of a bag, such as a money bag or mail bag. Several types of seals for this purpose are in common use, and comprise a plastic housing and a shackle, with a metal ferrule in the housing which, after the shackle has been passed through the housing and tightened around the bag, is crimped by a suitable tool to lock the shackle in the housing. However, for reasons of economy, it would be desirable that such seals be formed of a single piece of molded plastic.
Although several types of all plastic seals have been proposed for such use, none has achieved any substantial success because they have been found susceptible to removal and replacement by an unauthorized person without leaving evidence of tampering. Since the plastic of which the seal is formed is necessarily flexible, it is also stretchable, and in some cases the seal may be stretched enough to be slipped over the end of the bag and replaced onto the bag after some or all of the contents have been removed. In other cases the locking mechanism, which is formed of the same resilient plastic, may be released with a suitable tool without damage, and the seal may than be re-applied to the bag after the contents have been removed.
Another problem with such all plastic seals has been the fact that if the locking mechanism is made strong enough to resist tampering, it may be difficult to pull the shackle through the housing far enough to enable the end of the shackle to be grasped by the closing tool, which can be tiring to personnel who assemble hundreds of seals per day.